Restoring works of Takamatsu castle tower base were carried on. Restoration for historical structure with the value of cultural assets like Japanese castle requires keeping the authenticity of itself and reversible construction methods. On the works，in order to satisfy two requirements and also to improve the stability of the tower base masonry, geotechnical methods were applied. The measures for stabilization such as stabilization of lime and drainage for back fill, frame structure at the base stone were constructed based on results of some ground surveys and numerical analyses. These measures were very effective for the restoring of castle tower base masonry.
The tsunami deposits that were produced during the Great East Japan Earthquake are mixtures of various types of waste. They are classified as a specified item and disposed of as waste. The national guidelines stipulate that the tsunami deposits that meet all the requirements (e.g. requirements for separation and disposal and freedom from toxic materials) and have been identified by prefectural or municipal governments should not be classified as waste. Under the circumstances, tests were conducted concerning the applicability of the rotary crushing and mixing method (NETIS KT-090048-V) that had been adopted for soil improvement for the purpose of expanding the use of the method for separating and disposing of tsunami deposits and modifying the separated deposits into recycled materials for use in public works. Separating tsunami deposits that are in the form of soil mass using solely vibrating sieves is extremely difficult. It was found that deposits could be separated much better by crushing and grinding soil masses using rotary crushing and mixing machines. It was also became clear that making an effective use of concrete produced as disaster waste or crushing and mixing tsunami deposits using quicklime as an additive was highly effective for separating and disposing of deposits. As a result of adding concrete waste or quicklime for separating and mixing deposits, separation and mixing were improved and the trafficability was enhanced owing to the improvement of separated soils. The soils modified using the rotary crushing and mixing method were considered applicable as recycled fill materials. Thus, using the rotary crushing and mixing method enables the separation of tsunami deposits, which are generally disposed of as waste unless modified, into waste and deposits and the use of separated deposits as recycled materials. Removing the deposits attached to waste as much as possible is expected to contribute to the reduction of the quantity of waste that needs to be treated at disposal sites. Disaster waste will be disposed of at high speed in the affected areas. We propose the rotary crushing and mixing method as a useful method that can meet diverse requirements.
Bearing capacity of ground is important for any kind of construction. There are various kinds of instruments available for bearing capacity measurement. Recently, one portable test device for bearing capacity of ground has been developed and it gives similar results as of the plate load test. The portable test device can measure bearing capacity within a short period of time. But, there is always a concern about the accuracy of the device because load plate diameter of the device is smaller than that of the plate load test. According to the past experimental studies, the authors make it clear that there is a good correlation between the results of the portable test and the plate load test for the ultimate bearing capacity of cohesive soil. However, a similar verification test for the coarse grained soil is still not carried out, and its performance on a weak stratum near to surface of ground has not been examined yet. In this study, firstly the authors discuss the relationship between maximum grain size, compacted density, and ultimate bearing capacity obtained from the portable test device. Next the authors also determine the performance to identify the weak stratum by the portable test device. Then the portable test device and plate load test were carried out on same ground. As a result of this study, it became clear that the portable test device can identify ultimate bearing capacity of gravelly and sandy soil with maximum particle size of 10mm. Then the portable test can also detect the presence of weak layer on the ground by changing the plate diameter of device. Moreover, the relation between the ultimate bearing capacity of portable test and that of plate load test can be expressed in terms of the linear equation from the results of verification experiment carried out on same ground.
There are some counter measurements developed for sustaining liquefaction damage. Though the method is theoretically clear, only few example of application. In 1995, Hyogo Nanbu earthquake triggered the liquefaction in the urban and coastal area around Osaka bay containing Tsukiji area. Liquefaction caused many houses tilted, settled and collapsed around the lowland and reclaimed area. In this paper, some damaged structures caused by the liquefaction are introduced. It focuses Tsukiji area, which is about 12km far from the active fault line describing geological profile and ground water environment. Tsukiji area is where the dewatering method was applied as the counter measurement. Land subsidence was caused by pumping groundwater and it caused the leakage from the surrounding sea which has been a concern for local government. This paper shows how to decrease the groundwater level in the area by working from the design concept on installing the permeable pipe in the netlike based upon the site pumping test. As the result, 3m of non liquefaction layer over the groundwater was secured.
In this study, Hydraulic conductivity tests using a flexible wall permeameter were conducted using the improved soils by deep mixing method. The effects of whether measures are taken or not to prevent leakage through sidewalls on the results of permeability tests, and the condition that satisfied the condition of hydraulic conductivity k not exceeding 1.0 × 10-9m/s were investigated. As a result, it was verified that 1) taking measures to prevent the leakage through sidewalls is essential when conducting a flexible wall permeability test using the improved soils by deep mixing method and that 2) a correlation was recognized between the hydraulic conductivity k and unconfined compression strength qu of the improved soils by deep mixing method and k never exceeds 1.0 × 10-9m/s if qu is 2.0MN/m2 or higher.
Test embankment work was conducted in peat deposit to clear effect on reduction in secondary consolidation of the vacuum preloading method. The finite element analysis using an elasto-viscoplastic model was also conducted to evaluate the reduced secondary consolidation of peat. The following matters were clarified as a result ; 1) Negative pressure, which was applied during pump operation, was unloaded after the stopping of pumps and caused over consolidation of the ground. 2) The relationship between the overconsolidation ratio (OCR) and the reduction rate of secondary consolidation (R) describes a form close to a hyperbola curve. 3) Secondary consolidation can be controlled by vacuum preloading, and the amount of settlement can be predicted using the relationship between the OCR and R.
Sludge treatment at the water purification plant is classified into solar drying and pressure dehydration. Compared with the latter, the former can reduce an expense required for a device and facilities. On the other hand, the former has disadvantages in that the retrievement of sludge is after approximately one year because the drying rate of sludge including a large quantity of water depends on a season or the weather. We firstly performed a simple loading test to promote the water-reducing of sludge which was dried in the sun. In this experiment, we laid the sludge of nearly 460% water content onto geotextile fixed in a container of 100mm inside diameter, and added the normal stress of 0.10MN/m2 from 0.05MN/m2 for 24 or 48 hours. Water contents after the unloading have decreased to about 260% due to synergy of load and geotextile for the drainage promotion. This difference of the water content was almost corresponding to three months solar drying period. We secondly examined the bearing capacity and strength characteristics of specimens made by adding stabilizers into the sludge which was dried to nearly optimum water content. The results of California Bearing Ratio test, unconfined compression test and box shear test indicated that CBR value, unconfined compressive strength and shear strength all increased with lapse of the days, regarding the specimens cured in water upon the neck of air. The consequence that the strength developed in proportion to the common logarithm of curing days was also obtained, from the unconfined compression test of specimens cured only in air for 90 days. As above, it can be considered that shortening a solar drying period to heighten the desludging frequency contributes to an improvement in the operating ratio of air drying bed and a cyclic utilization of resources.
When the strength of earth is so low that the earth is not able to maintain the upper structure, soil improvement methods such as cement mixing are generally recommended. In an unconfined compression test for deciding cement volume and confirming the strength of soil improvement, the mean value of test results of three samples are generally used, although the dispersion of the three test results are left out of consideration. Recently, the estimation method of dispersion for test results is discussed internationally and the notation of dispersion is united under the term “uncertainty”, which is used in many fields of industry, medicine, agriculture and so on. As the Japanese Industrial Standard, the estimation methods of uncertainty are necessary to testing and calibration laboratories. In this thesis, firstly the estimation method of the uncertainty of compression test results of cement mixing soil is presented by the analyses of verification experiments on causes of dispersion. Next, it makes clear that the uncertainty of test results is able to be estimated by the proficiency test that evaluates the test result of a laboratory in comparison with results of many laboratories. The uncertainties of the two methods above show that the measuring equipment and testing apparatus do not affect uncertainty, and the influence of the operator (laboratory) and the difference of samples are conversely large.
In construction, chemical soil stabilization method, such as adding cement and quick lime has been often applied to increase the strength of soft ground and surplus soil. However, in some specific natural environments, such a stabilization method may cause significant reduction of the strength of treated-soil. In this paper, Ordinary Portland cement was used as a stabilizer for examining the durability of chemical stabilized Ariake clay under seawater condition. In order to prepare deteriorated specimens, original Ariake clay was mixed with different contents of cement (50, 70, 100kg/m3) and immersing artificial seawater with different NaCl concentration (10, 20, 30g/L). The deterioration progress of cement-treated Ariake clay was investigated by using the micro cone penetration test. It is shown from the test results that the deterioration of cement-treated soil progresses in proportion to square root of seawater contacting duration. In addition, an empirical prediction formula of deterioration rate of cement-treated Ariake clay considering effect of Mg ion concentration in seawater and water-cement ratio in the treated soil is proposed according to experimental results.
In the quality assurance procedures of cement-treated soil columns, it is important to evaluate appropriately the behavior of the full scale column from the cored sample strengths. This paper presents the numerical method that can predict the unconfined compressive behavior of a cement-treated soil column from which cored samples are retrieved. The finite element method with Monte Carlo simulation was used to investigate the compression behavior of the full scale column with spatial variability. A conditional simulation was conducted to evaluate the compressive strength of the full scale column with the fixed data values. A unconditional simulation without the fixed data values was also conducted for comparison. Results obtained in this study suggest that the conditional simulation offers benefits over the unconditional simulation for evaluating the overall strength of the cement-treated column from which the cored samples are retrieved.
Due to the wide spread of soft soil in Japan, different cement stabilization methods have been used to improve the soil property. Recently, the waste disposed by many industrial plants has been utilized effectively by cement stabilized method. The typical example is the utilization of disposed coal ash by thermal power plants. Currently, effective utilization of coal ash depends on cement raw materials. Under the situation of public work projects declines, it has led to the decreasing demand for cement. The cement stabilized soil will be excavated for construction work in future and reused. The excavated cement stabilized soil is usually resulted from road maintenance and repair of lifeline such as water and gas pipes. However, the excavated cement stabilized soils have been disposed due to the unknown characteristics of these materials. Therefore, studies on excavated cement stabilized soil should be carried out in order to encourage the recycling-oriented society. Correspondingly, this study deals with recycling and reusing of cement stabilized soil and/or cement stabilized soil mixed with coal fly ash, and examining the effect of reusing of cement stabilized soil on strength characteristics. The results of this study show the possibility of reusing of cement stabilized soils as alternative construction material.
This paper estimates the durability of water-swelling materials that is an important element in water cutoff performance of vertical cutoff walls constructed in coastal waste landfill sites. We carry out accelerated deterioration tests on the water-swelling materials. Furthermore, we predict the durability of water-swelling materials based on Arrhenius law. When Arrhenius law is applied to the result of accelerated deterioration test, the life of water-swelling materials will be estimated about 27 years. This suits the previous results in which decreasing in strength of water-swelling materials will not advance after progress from their curing start for one year. Therefore, it is thought that water-swelling materials are utilizable enough as water cutoff materials of vertical cutoff walls constructed in waste landfill sites for tens of years.
When excavation works are executed at stratums that naturally contain heavy metals due to their geologic histories, time-saving and reliable assessment of contamination potential by the metals and metalloids in excavated soil/rock is required. Leaching of heavy metals from excavated rocks is influenced both by physical factors (crushing, exposure to water, temperature) and chemical factors (oxidation, soil-water interaction, pH change, etc.). This manuscript addresses long term leaching behavior of arsenic and lead affected by these factors, which were determined by outdoor exposure tests. The tests were conducted on the excavated rock samples weathered outdoors for more than two years. In addition, several time-saving laboratory tests for characterizing the contamination potential of arsenic and lead were validated by comparatively assessing the results of the outdoor exposure tests, to develop some simple evaluation methods of contamination potential of excavated rock containing heavy metals.